Capacitive pressure sensor and method of manufacturing same

Abstract

This rugged, temperature-shock-insensitive, and low-cost pressure sensor (1) has a diaphragm (2) and a substrate (3) which are alumina-ceramic parts, preferably with a purity of 96%, are joined together in a defined spaced relationship and parallel to each other by means of an intermediate layer, forming a, preferably closed, chamber, and have flat inner surfaces which are provided with at least one conductive layer for forming at least one capacitor and are electrically connected to the respective rear side of the diaphragm or substrate via through-hole coatings. For the conductive layers (6, 7, 8), the through-hole coatings (12, 13, 14), and the intermediate layer (5), use is made of a conductive paste or a resistive paste with a sheet resistivity not higher than 1 ohm/square, which are applied using silk-screening techniques.

What is claimed is: 
     
       1. A method of manufacturing a capacitive pressure sensor comprising a diaphragm and a substrate which are joined together by an intermediate layer in a defined spaced relationship, substantially parallel to each other, and forming a chamber therebetween, said diaphragm having a flat inner surface and at least one first conductive layer formed on said inner surface and said substrate having a flat top surface facing the inner surface of the diaphragm and at least one second conductive layer formed on said top surface, the at least one first conductive layer and the at least one second conductive layer cooperating to provide at least one capacitor therebetween, at least one of the first or second conductive layers being electrically coupled to at least one through-hole coating formed on at least one aperture extending through the diaphragm or substrate, the method comprising the steps of: applying a conductive or a resistive paste having a uniform composition to the substrate and diaphragm by printing using silk-screen techniques to form said at least one first and second conductive layers, said at least one through-hole coating, and said intermediate layer, said paste being applied by the steps of:   printing the paste in desired areas of the substrate and diaphragm in a thickness suitable to form said at least one first and second conductive layers and forcing the paste into at least one hole provided int he diaphragm or substrate to form said at least one through-hole coating,   waiting for the applied paste to dry,   printing an additional paste layer having a predetermined thickness in the area of said intermediate layer to form said intermediate layer,   waiting for the additional paste layer to dry,   placing said coated diaphragm on top of said coated substrate, and   firing the diaphragm and substrate to bond the diaphragm to the substrate to form the capacitive pressure sensor.   
     
     
       2. The method of claim 1, wherein the diaphragm and substrate are formed from an alumina-ceramic material. 
     
     
       3. The method of claim 2, wherein the alumina-ceramic material has a purity of 96%. 
     
     
       4. The method of claim 1, wherein the step of forcing the paste into the at least one hole to form said at least one through-hole coating includes drawing the paste into said at least one hole by applying a vacuum to the at least one hole. 
     
     
       5. The method of claim 1, wherein the conductive or resistive paste has a sheet resistivity less than or equal to 1 ohm/square. 
     
     
       6. The method of claim 1, wherein the conductive paste does not include any glass. 
     
     
       7. A capacitive pressure sensor comprising a diaphragm having an outer surface and a substantially planar inner surface,   a substrate including a top surface facing the inner surface of the diaphragm, the substrate being formed to include at least one aperture extending therethrough in communication with the top surface,   a first conductive layer formed on the inner surface of the diaphragm,   a second conductive layer formed on the top surface of the substrate,   a third conductive layer configured to line said aperture extending through the substrate, the third conductive layer being electrically coupled to the second conductive layer, and   an intermediate layer for coupling the diaphragm to the substrate to position the inner surface of the diaphragm a predetermined distance away from the top surface of the substrate to provide a capacitor therebetween formed by the first and second conductive layers, the intermediate layer and the first, second, and third conductive layers being formed from a material having a uniform composition.   
     
     
       8. The sensor of claim 7 further comprising a fourth conductive layer formed on the top surface of the substrate surrounding the second conductive layer and spaced apart from the second conductive layer to form a second capacitor with the first conductive layer, the substrate being formed to include first and second apertures extending therethrough, the third conductive layer being configured to line the first aperture, the third conductive layer being electrically coupled to the second conductive layer, and a fifth conductive layer being configured to line the second aperture extending through the substrate, the fifth conductive layer being electrically coupled to the fourth conductive layer, the fourth and fifth conductive layers being formed from the same uniform configuration material as the intermediate layer and the first, second, and third conductive layers. 
     
     
       9. The sensor of claim 8, wherein the substrate is formed to include a third aperture extending therethrough, and further comprising a sixth conductive layer configured to line said third aperture extending through the substrate, the sixth conductive layer being electrically coupled to the intermediate layer and the first conductive layer, the sixth conductive layer being formed from the same uniform composition material as the intermediate layer and the first, second, third, fourth, and fifth conductive layers. 
     
     
       10. The sensor of claim 7, wherein said material having a uniform composition includes a conductive or resistive paste. 
     
     
       11. The sensor of claim 10, wherein the conductive or resistive paste has a sheet resistivity less than or equal to 1 ohm/square. 
     
     
       12. The sensor of claim 10, wherein the conductive paste does not include any glass. 
     
     
       13. The sensor of claim 10, wherein the conductive paste is applied to the diaphragm and substrate using silk-screen techniques to form said first, second, and third conductive layers and said intermediate layer. 
     
     
       14. A capacitive pressure sensor comprising a diaphragm having an outer surface and a substantially planar inner surface,   a substrate including a top surface facing the inner surface of the diaphragm,   a first conductive layer formed on the inner surface of the diaphragm,   a second conductive layer formed on the top surface of the substrate,   an intermediate layer for coupling the diaphragm to the substrate to position the inner surface of the diaphragm a predetermined distance away from the top surface of the substrate to provide a capacitor therebetween formed by the first and second conductive layers, the intermediate layer and the first, second, and third conductive layers being formed from a material having a uniform composition.   
     
     
       15. The sensor of claim 14, wherein the substrate is formed to include an aperture extending therethrough in communication with the top surface, and further comprising a third conductive layer configured to line said aperture extending through the substrate, the third conductive layer being electrically coupled to the second conductive layer through the aperture, the intermediate layer and the first, second, and third conductive layers being formed from the same material having a uniform composition. 
     
     
       16. The sensor of claim 15, further comprising a fourth conductive layer formed on the top surface of the substrate surrounding the second conductive layer and spaced apart from the second conductive layer to form a second capacitor with the first conductive layer, the substrate being formed to include first and second apertures extending therethrough, the third conductive layer being configured to line the first aperture, and a fifth conductive layer being configured to line the second aperture extending through the substrate, the fifth conductive layer being electrically coupled to the fourth conductive layer through the second aperture, the fourth and fifth conductive layers being formed from the same uniform composition material as the intermediate layer and the first, second, and third conductive layers. 
     
     
       17. The sensor of claim 16, wherein the substrate is formed to include a third aperture extending therethrough, and further comprising a sixth conductive layer configured to line said third aperture extending through the substrate, the sixth conductive layer being electrically coupled to the intermediate layer and the first conductive layer through the third aperture, the sixth conductive layer being formed from the same uniform composition material as the intermediate layer and the first, second, third, fourth, and fifth conductive layers. 
     
     
       18. The sensor of claim 14 wherein said material having a uniform composition includes a conductive or resistive paste. 
     
     
       19. The sensor of claim 18, wherein the conductive or resistive paste has a sheet resistivity less than or equal to 1 ohm/square. 
     
     
       20. The sensor of claim 18, wherein the conductive paste is applied to the diaphragm and substrate using silk-screen techniques to form said first and second conductive layers and said intermediate layer.